Recent years, a tablet type terminal device becomes compact and thin so as to be easily carried by a user. The compact and thin terminal device may not have an expanded function such as an external interface. In this terminal device, the terminal device is connected to an expansion device such as a cradle or a docking station having expanded functions, and then, the functions of the expansion device are used.
The terminal device and the expansion device can communicate with each other by making the connection terminals of both terminals come in electrically contact with each other at the time of connection. If the connection terminals are energized when disconnecting the terminal devices from the expansion device, in some cases, the connection terminals may deteriorate due to an occurrence of a spark between the two terminals. Therefore, for example, a technology is known, in which a magnetic sensor is provided in the terminal device, and the magnetic sensor detects a magnetic field using a magnet attached to the expansion device, and a power supply to the connection terminals is cut off according to the change of the magnetic field (for example, refer to Japanese Laid-open Patent Publication No. 2009-157877). As another related art, for example, Japanese Laid-open Patent Publication No. 6-161611 is disclosed.
However, in the Patent Literatures described above, in order to detect the change of the magnetic field, the terminal device is desired to be removed. Therefore, it is not possible to realize the cutoff of the power supply before removing the terminal device. In this case, a spark occurs when removing the terminal device from the expansion device, and thus, the connection terminal may deteriorate.